Disposable absorbent products like diapers typically include stretchable materials in the waist, cuff, and other regions to provide a snug fit and a good seal of the article. Pant-type absorbent articles may further include stretchable materials in the side portions for easy application and removal of the article and for sustained fit of the article. Stretchable materials have also been used in the ear portions for adjustable fit of the article. The stretchable materials utilized in these article regions may include elastomeric materials such as films, nonwovens, strands, scrims, and the like. In most cases, these designs deliver uniform and unidirectional stretch, most often in the lateral direction of the article. However, elastomeric materials are relatively expensive so their use in stretchable materials is desirably optimized. Additionally, if elastomeric materials are used without some type of cover material, the elastomeric materials may tend to exhibit increased drag on skin surface, which may result in discomfort to the wearer of the product.
Stretchable materials may be made in the form of a stretch laminate, which involves one or more elastomeric materials laminated to one or more layers of another material. While the laminate may improve wearer comfort, the laminate may exhibit more limited stretchability and/or considerable resistance to stretch. Several approaches exist addressing this resistance to stretch.
One approach for creating stretch laminates is by a stretch bonding method. Stretch bonded laminates are made by stretching an elastic in a first direction, bonding the stretched elastic to one or more materials such as a nonwoven, and releasing the tension from the elastic so that the materials gather. The resulting laminate typically will be extensible in the same direction in which the elastic was stretched. The gathered nonwoven tends to have a corrugated feel and increased caliper that can improve wearer comfort when such stretch bonded laminates are used in absorbent products. The gathered nonwoven may also exhibit improved opacity; a feature that may be desirable since improved opacity often suggests a high quality product.
The elastic may be supplied to the stretch bonding process (e.g., elastic strands purchased from a supplier) or formed in-situ within the process. Having the elastomeric material supplied to the process is not without problems. A problem with supplying elastomeric materials to the process is that processing flexibility is reduced. Any modification to the elastomeric material requires sufficient lead time so that the required elastomeric materials may be ordered, formulated, produced, shipped, and integrated. Having elastomeric material formation as an in-situ or in-line element to the stretch bonding process may address some of the supply problems; however, current in-process elastomeric material formation methods present a variety of processing difficulties.
A common problem with in-process formation of stretch laminates involves the structure and form of the elastomeric material. Typical elastomeric material formation involves extrusion of a molten elastomeric composition through an apertured die. The extrusion process limits the available compositions that may be extruded and the shapes and/or structures that may be extruded. The shape of the resulting elastomeric material may be dictated by the shape of the aperture within the die. Since the aperture is a fixed shape and dimension, the resulting elastic materials drawn through the aperture will typically be of a fixed shaped and dimension (i.e., a circular aperture will yield an elastic strand having a circular cross-sectional shape throughout the length of the strand). Thus, structural variability in extruded elastomeric materials may be difficult to achieve.
Extrusion also limits processing flexibility as to the elastomeric compositions that may be used. The extrusion of an elastomeric composition results in several unique processing challenges. For example, extrusion may present problems with regard to surging or draw resonance of the elastomeric composition. Both of these problems may be addressed by adjusting the formulation of the elastomeric composition. However, such adjustments to the elastomeric composition may, in turn, limit the structural or functional properties (e.g., modulus, tensile strength, etc.) of the resultant elastomeric materials.
Another problem that is seen with in-line extrusion of an elastomeric composition involves the maximum line speed that may be achieved. Extrusion may often be the bottle-neck in the process line. The quantity of elastic materials available to be stretch bonded may be ultimately limited by the amount of elastomeric composition that can be drawn through an apertured die. This through-put is variable depending upon such properties as the formulation of the elastomeric composition and the size and shape of the apertures. However, any given extrusion process traditionally yields a maximum through-put. Limits on the through-put of elastomeric composition through the apertured die are translated into reduced quantity of elastomeric material per unit time which then results in a reduced quantity of stretch bonded laminate per unit time.
An alternate approach of creating stretchable materials is disclosed in copending U.S. application Ser. Nos. 10/288,095, 10/288,126, and 10/429,433. This approach involves hot melt application of one or more thermoplastic elastomers onto a substrate (e.g., nonwoven), followed by incremental stretching of the substrate that confers the stretch properties of the elastomer to the substrate in a somewhat magnified form. This method allows for the deposition of any amount of an elastomer in any shape and direction, thus giving a wide variety of design flexibility which ultimately results in improved fit of the overall diaper product. However, the hot melt application method can be improved. Incremental stretching can physically break the fiber to fiber network within a nonwoven. As a result, an incrementally stretched nonwoven may appear shredded and be aesthetically undesirable. The shredded appearance can be avoided by using a nonwoven with a sufficiently high basis weight, but with increased basis weight comes increased cost. Furthermore, it is difficult for the hot melt application method to yield a stretch laminate that exhibits a gathered appearance as found in stretch-bonded laminates. Without a gathered nonwoven, the benefits of corrugated feel and increased caliper are missing. Furthermore, the opacity of stretch laminates resulting from the hot melt method can exhibit reduced opacity as compared to a like stretch bonded laminate (i.e., the stretch bonded laminate and hot melt laminate having nonwovens of like construction and basis weight).
In view of the above, it would be desirable to provide a cost effective stretch laminate comprising elastomeric materials that may be produced in-process without one or more of the aforementioned problems. It would be desirable to use such stretch laminates within specific areas of absorbent articles such as diapers and the like to provide a desired in-use benefit (e.g., sealing, containing, gasketing, body-conforming) for the article. It would also be desirable to provide an efficient and cost-effective process for producing the stretch laminates. Further, it would be desirable to provide a process for producing stretch laminates that do not require the use of externally supplied elastic members or in-process extrusion formed elastic members.